1. Field of the Invention
This invention relates to a CDMA communication system, and more particularly to an apparatus and a method for securing a communication information in a CDMA communication system, thereby enabling the system to communicate privately with no overhearing.
2. Description of the Related Art
In a conventional CDMA communication system according to the IS-95 standard, a voice is encoded as an information bit by a vocoder (a voice encoder/decoder) and modulated in a reverse traffic channel. The modulated signal is transmitted to a base station. The modulated signal from the base station is reproduced as the original information bit in a forward traffic channel and it is decoded as an original voice by a vocoder. By the above process, it is possible to communicate between the remote mobiles.
However, the conventional CDMA system has the disadvantage that the information bit passing through only the vocoder can be detected at the base station or at a switching system, and the detected information bit can be easily decoded as the original voice. Thus, the conventional CDMA system has weakness for an overhearing.
U.S. Pat. No. 5,727,064 discloses the technique for solving the disadvantage, wherein a scrambler is added to a longcode generator. But, the technique can not be applied to the conventional CDMA system without any change because it requires the modification of IS-95 CDMA facilities, and it has a limit to communicate between the different user groups using the different security keys.